Lenses are used for a variety of purposes, for example in eyewear (such as spectacles and sunglasses) and in optical devices such as microscopes, cameras and telescopes. The use of plastic materials to prepare ophthalmic lenses for use in vision corrective and prescription (Rx) spectacle lenses, as opposed to traditional glass lenses, has increased dramatically due to various advantages of plastic lenses over glass lenses. Amongst other things, such plastic lenses can be made scratch and abrasion resistant and can be provided in a wide range of fashionable colours.
The use of polycarbonate as the plastic material has recently become attractive, compared to the commonly used polymers based on allyl diglycol carbonate monomers (such as CR-39™ available from PPG Industries Inc). Indeed, due to the advantageous properties of polycarbonate, the adoption of polycarbonate as a lens material has seen the development of different lens shapes and configurations, such as the steeply curved lenses described in international patent application PCT/AU99/00430. It has also seen the continuation of interest in rimless spectacle frames, rimless spectacle frames being far more practical for plastic lenses than for glass lenses.
However, such developments have resulted in the peripheral edge of lenses (being the edge bound by the front and back optical surfaces of a lens) sometimes being thicker than normal and also being more visible when in use in eyewear. Indeed, in rimless spectacles, not only will the edge be visible (thus requiring the consideration of aesthetic issues such as colouring the edge for fashion purposes), it will also be subject to the same likelihood of scratching or chipping as would one of the optical surfaces of the lens.
In U.S. Pat. No. 4,076,863 an edge coating process is described wherein a resin material is applied to an edge of a lens and subsequently polymerised. Similarly, U.S. Pat. No. 5,220,358 describes a process whereby an edge of a lens is coated with a dimethyl silicone coblocked with cross-linked vinyl. In each of these cases the coating material needs to be applied carefully to the edge of the lens in order to minimise over-run of the material onto optical surfaces of the lens. This is a time consuming process.
Accordingly, there is a need for a method of coating the edge of a lens (for instance, so as to protect or colour the edge) that overcomes problems with known methods, and it is an aim of the present invention to provide such a method.